SU1337965A1 - Method and device for protecting the distributing electric mains with nonlinear load and power filter against overloads by resonance-frequency currents - Google Patents

Description

The invention relates to electrical engineering, in particular power supply of industrial enterprises, and can be used to protect 6-20 kV distribution networks supplying loads with nonlinear characteristics: AC and DC thyristor electric drives, steelmaking and arc furnaces, etc.

A device is known for introducing an emergency component of an electrical quantity in the event of a damaged electrical network, containing an input three-phase adder connected by an input to a sensor of a monitored signal, block for calculating corrections, two outputs of which are connected via integrators to two inputs of a three-phase sinusoidal integrator whose output is connected to the inverted input of the specified sum (ator and the first additional input of the correction block, the frequency correction block, included between the outputs one from about integrators and the third input of the sine wave generator, which detects the avarsh | H that was Yusch that current and last dostizheppi za- dayuyuy nelichipy gives a signal to the damaged portion otklyuchimte CE ti SP.

The disadvantage of the device for the protection of the distribution network is that it is insensitive to the occurrence of resonance in the field between the network’s performance and the capacitor battery capacity (KB) connected to the filter networks, if at the same time Bn / ie thyristor converters and : 1 and metallurgical furnaces. During operation, the filter can be detuned from its resonant hour 1 due to a change in the inductive and capacitance of the filter resistances as the temperature and frequency of the supply mains change, as well as the failure of individual capacitors or inter-turn short circuits in the filter reactor. With a capacitive detuning of the filter, a significant increase in the dust harmonic current in the filter circuit and the power supply network is possible compared to the total current of the same rapMOHitK consumer with a nonlinear characteristic. At the same time, the engine is equipped with

power strips are underutilized in power due to the appearance of large negative-sequence currents, a; capacitors, power cables, n reactors overheat, i.e. it becomes necessary to disable the filters.

The known method of protection of the distribution network, in which the overcurrent is measured, high harmonics are extracted in normal and emergency modes, and if the specified values deviate from the predetermined values, the network is disconnected with time acceleration C2. containing a network current sensor, a current relay whose setting is adjusted according to the sensitivity condition, as well as a high harmonic filter, a NO block and two OR elements, a time relay, and a pair is turned on at the current sensor output allel current relay and filter

 HLicuii-fx harmonics-, on which code a logical circuit is assembled, providing disconnection of the damaged part of the network without time lag 2.

30 il "j; ocTaTKaMH of the known method and ycTpoiiCTBa are the insensitivity of the protection of the distribution network to the occurrence of resonance between the network inductance and the capacitance

35 capacitor battery connected to the network of filters; the nonselectivity of this method of protection in networks with consumers who have non-linear testing, because the level of higher

40 harmonics and, consequently, the search ratio of the consumed current in normal modes is much more pronounced than with short-to-curtain (CC) on the 0.4 kV side connected to this network

45 1 ranformator. Therefore, when short circuit

0.4 kV side, simultaneous shutdown of the distribution network without time delay occurs.

The purpose of the invention is to increase the reliability of operation by increasing the supply capacity and selectivity of protection.

The goal is achieved by the fact that in the method of protecting a distribution network with a nonlinear characteristic of the load and a power filter from overloading the currents of the resonance frequency, by which the current of the power grid is measured, the frequency of the resonant frequency in it is 313

You can compare the selected component with the iiop task (iroM and, if its selected component is exceeded, generate a signal to turn off the power filter, additionally measure the current of the said non-linear load, allocate a resonant frequency current to B) and use this selected component as a threshold.

In a known device for protection of a distribution network with non-linear load and a power filter against overloading of resonant frequency currents, in each of the three phases there is a first sensor of the power network connected to its output by the first high-harmonic filter, an actuator, and an input unit The first integrator and the first rectifier are connected to the output of the high harmonic filter through the serial input, the first integrator and the first rectifier, additionally introducing the second current sensor in the circuit a linear load with a second harmonic filter connected to its output, the output of which is through a rectifier and a second connected via a series of BTopoii. The integrator is connected to the second input of the mentioned comparator unit, and the output of the said executive body is connected to the disconnecting input of the switch in the power filler circuit.

The essence of the proposed method of protecting a distribution network with a power filter and a nonlinear load characteristic is that they separate the current of the frequency of tuning the network and the load source, compare the values of the selected resonant currents, turn off the power filter when the current of the resonant harmonic in the distribution network of this harmonic is exceeded, flowing in the load circuit.

The drawing shows a structural diagram of the protection device of a distribution network with one power filter and a load in the form of an arc furnace and a thyristor electric drive, which have highly non-linear characteristics.

The device contains a current sensor 1 {current transformer of a distribution network 2, a current sensor 3 in the load circuit 4, each of the current sensors through the corresponding filters 5 and 6

five

VYP1IH rapMoiKTK, rectifiers 7 and 8 and integrators 9 and 10 are connected1 1 separately to the inputs of a comparing node 11, the output of which is connected through an actuator 12 to a control switch 13 connected in series with the power supply 14. Protection of the distribution network from

power filter and nonlinear load characteristic is as follows.

When a consumer operates with a nonlinear characteristic, for example, a valve electric drive, a reactive trash is consumed from the network and the form of the supply current is distorted by switching in the converter. In the absence of power filters, the current in

distribution network is identical to the current in the load circuit, and hence the currents of higher harmonics in the network and the load circuit are equal to each other.

When connecting the power filter,

tuned to one of the harmonics, the value of the resonant harmonic current in the network is reduced, since for the said harmonic the ideal filter is low resistance.

The degree of filtering is determined by the quality factor of the power filter, the quality of its tuning into resonance, and depends on the ratio of network power and installed capacity of the capacitor battery of the filter.

During operation, a detuning of the power filter is possible, which may be caused by a change in inductive or capacitive impedance.

cells with changes in the temperature and deviations of the mains frequency from the nominal, as well as due to inter-turn short circuits in the reactor, failure of individual fuses in a capacitor battery, etc.

When a power filter is operating in a distribution network with a non-linear consumer characteristic in the case of

its capacitance detuning current resonance} harmonics in the network can significantly exceed the current harmonics in the load circuit.

A similar amplification of the resonant or nearby harmonics can occur with and ;; a tuned filter due to the parallel resonance of the inductance of the network with the capacitance of the capacitor battery, if the distribution of the distribution network and its resistance change in an uncontrolled manner. However, in both the first and second cases, the resonant harmonic current of the load circuit remains almost unchanged, while the current in the electrical network increases.

and 3 current set

Using sensors I (current transformers), non-sinusoidal currents are measured in the distribution network 2 and the load circuit 4. At the output of current sensors 1 and 3 to highlight the resonant harmonics

79ft5

Kklkcheyy filters 5 and 6 respectively.

The selected resonant harmonics are then rectified by rectifiers 7 and 8, and then the rectified values of the resonant harmonics are integrated by integrators 9 and 10 to eliminate pulsations and compared by 10 using Comparison Unit II. When a current harmonic in the distribution network of a high harmonic current flowing in the load circuit is exceeded, the actuator 12, 15 operates the switch 13 in the power filter circuit 14, thereby increasing the reliability of operation.

yy

Editor M. Dylyn

Compiled by V. Molchanov Tehred L. Oliynyk

Order 4138/51 Circulation 617 Subscription

VNISh State Committee of the USSR

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Production and printing company, Uzhgorod, st. Project, 4

12

72

Proofreader M. Demchik

Claims (2)

METHOD FOR PROTECTING A DISTRIBUTION ELECTRIC NETWORK WITH NONLINEAR LOAD AND POWER FILTER FROM RESETTING CURRENT RESONANCE FREQUENCY CURRENTS AND DEVICE FOR ITS IMPLEMENTATION 1. A method of protecting a distribution network with a non-linear load and a power filter from overloading with resonant frequency currents, which measure the current of the network, isolate it, the resonant frequency current, compare the selected component with a predetermined threshold and, if its selected component is exceeded, form a signal to turn off the power filter, characterized in that, in order to increase the reliability of operation by increasing the sensitivity and selectivity, additionally measure the current of the aforementioned non-linear load loads, emit in it the magnitude of the current of the resonant frequency and use this selected component as the mentioned threshold. 2. A device for protecting a distribution network with a non-linear load and a power filter from overloading with resonant frequency currents, containing in each of the three phases a first mains current sensor with a first higher harmonic filter connected to its output, an actuator connected to its input, a comparison unit, to the first input of which, through the series-connected first integrator and the first rectifier, the output of the first higher harmonics filter is connected, characterized in that, in order to increase the sensitivity of the device two, a second current sensor was introduced in the nonlinear load circuit with a second higher harmonic filter connected to its output, the output of which through a second rectifier and a second integrator connected in series is connected to the second input of the said comparison unit, and the output of the said actuator is connected to the disconnecting input of the switch in power filter circuit. SU,. „1337965 I 33 7 965